Project Summary This proposal investigates the regulation of three selected genes that encode proteins that are critical for anaphylaxis that is mediated by IgE and mast cells (MCs). MCs release inflammatory mediators, including histamine, in response to antigen crosslinking of the IgE/FceRI complex; these mediators play a major role in causing IgE-mediated anaphylactic shock. Although much is known about the proteins that are involved in MC activation, signal transduction and mediator synthesis, little is known about how the genes that encode these critical proteins are regulated. We and others have demonstrated that the transcription factors (TFs) GATA2 and MITF are essential for MC development and maintenance. However, it remains largely unexplored how these and additional TFs interact with their target enhancers to regulate the expression of target genes that are important in mediating histamine synthesis, MC activation, and IgE-mediated disorders, including anaphylaxis and food allergy. Our long-term goal is to enhance fundamental understanding of the regulation of MC genes that influence food allergy susceptibility and severity. Our central hypothesis is that GATA2 and MITF detect MC activation signals, induce chromatin accessibility in genes essential in the anaphylactic pathway, and recruit other TFs to form a promoter/enhancer transcription complex that activates Hdc gene transcription in a switch-like manner (Hdc encodes histidine decarboxylase, the rate limiting enzyme in histamine synthesis). This central hypothesis is strongly supported by our preliminary data and will be tested in 3 aims that are conceptually innovative and make use of innovative technology. In Aim 1, we will determine how the TFs GATA2, MITF, MECOM and their target promoters and enhancers regulate the expression of Hdc and two other genes that are essential in the IgE/MC-mediated anaphylactic pathway: Fcer1a, which encodes the IgE- binding chain of the high affinity IgE receptor, and Pi3p85, which encodes the P85 regulatory chain of PI3K kinase, a signaling molecule required for MC degranulation. In Aim2, we will identify the enhancers and their associated TFs that regulate these genes in humans. In Aim3, we will analyze the function of Hdc enhancers in IgE/MC-mediated anaphylaxis. Upon completion of the planned studies, we will understand substantially more about the mechanisms through which MCs mediate anaphylaxis in both mouse and human. The acquired knowledge should promote understanding of gene regulation in general and the regulation of genes that influence food allergy susceptibility and severity in particular. As a result, these studies should promote the development of effective interventions to prevent and treat food allergy and other IgE-mediated allergic disorders.